Centrifugal casting apparatus



p 1957 A. A. BOSNA GENTRIFUGAL CASTING APPARATUS 2 Sheets-Shaet 1 Filed July 15, 1954 FIG.

JNVENTOR.

Alexandr A ,Basrm ATTORNEYS A. A. BOSNA CEWIRIFUGAL CASTING APPARATUS Sept. 10, 1957 2 Sheets-Sheet 2 Filed m 15, 1954 FIG. 7

- -INVENTOR. fll'exa'm/er :9. java BY Z34, \LLMJL' PIjOTO-ELECTRIG CONTROL CIRCUIT ATTORNEY-s United States Patent @ffrce asserts CENTRlF-UGAL CASTiN-G arranarns Alexander A. Bosna, Hichsville, N. Y., assignor, by mesne assignments, to .l'eltils Company, New York, N. Y a partnership Application July 15, 1954, Serial No. 443,547

6 tllaims. (Cl. 22-651) This invention relates generally to improvements in casting apparatus and, more particularly, to improvements in centrifugal casting apparatus of the type especially adapted for use in jewelry and dental work, and in the manufacture of small precision articles.

The primary object of the present invention is the provision of a centrifugal casting apparatus which will automatically cast at a predetermined and exact temperature.

Another object is the provision of a centrifugal casting apparatus which, by the elimination of the human elements involved, for example, in the reading of a temperature indicator, or in the manual release of the casting apparatus, is effective to provide castings of superior consistency and uniformity, each time the apparatus is operated.

In accordance with the foregoing objects, another object is the provision of photo-electric control means operable at a predetermined furnace temperature to release the casting apparatus for rotation thereof to provide a casting operation.

Another object is the provision in a centrifugal casting apparatu of a highly novel and automatically operable latching device.

Another object is the provision of an alarm means which is energized a predetermined time period prior to the unlatching of the centrifugal casting apparatus to provide a warning to the operator.

A further object is the provision of an i. proved furnace construction which facilitates the loading of the metal therein and also increases the capacity thereof.

A still further object is the provision of a generally improved centrifugal casting apparatus which is simple in design and construction, reliable in operation, and which is eminently suitable for the production of high quality precision castings.

The above and other objects, features and advantages of the present invention will be more fully understood from the folowing description considered in connection with the accompanying illustrative drawings.

In the drawings, which illustrate the best mode now contemplated by me for carrying out my invention;

Fig. 1 is a top plan view of a centrifugal casting apparatus according to the present invention;

Fig. 2 is a side elevation of the casting apparatus;

Fig. 3 is a fragmentary view taken in the direction of the arrow 3 in Fig. 2;

Fig. 4 is a perspective view of a latch arrangement for th centrifugal casting apparatus, portions being illustrated in section;

Fig. 5 is a sectiona View, on an enlarged scale, taken on the line 5-5 of Fig. 1;

Fig. 6 is a sectional view, on an enlarged scale, taken on the line 66 of Fig. 2;

Fig. 7 is a partial sectional view taken on the line 7-7 of Fig. 6; and

Patented Sept. 10, 957

Fig. 8 illustrates a schematic wiring diagram for the apparatus of the present invention.

Referring to the drawings in detail, the centrifugal casting apparatus 10 is of the general type shown and described in the patent to Herbert R. Berger, No. 2,245,065, dated June 10, 1941, and in my copending application Serial No. 429,012, filed May ll, 1954, now Patent No. 2,752,650, granted July 3, 1956, both of which are assigned to the assignee of the present invention. As illustrated and described in the aforementioned patent and application, and as here shown, the centrifugal casting apparatus 10 comprises a base 12 in which there is disposed a spring motor, or any other suitable source of power, which is adapted to rotate the shaft 14 at high speed. Said shaft has a horizontally disposed longitudinally extending bar or member 16 which is detachably secured thereto by a nut is threaded onto the upper end of the shaft which extends through the bar 16. The bar 16 is provided with a transversely extending slot 20 which is adapted for the reception of the transverse pin 22 carried by the shaft 14, it being understood that on the assembly of the bar 16 to the shaft 14, the pin will register in the slot 2d, whereby to positively key the bar 16 to the shaft 14. An insulator plate 24, which overlies the base 12, is suitably secured to the bar 16 for rotation therewith. Said plate is provided, at its lower surface, with the concentric pairs of conducting rings 2626 and 28-28. in order to make electrical contact with said rings, during the rotation of the bar to, provision is made in the base 12 for the brush assemblies 3ii3t; and 3232 which cooperate with the rings Z625 and 2828, respectively, as best illustrated in Fig. 5. More specifically, the brush assemblies 3fl3ii are constituted by the brush members which project from and are slidably mounted in an insulator plate 36 provided on the upper surface of the base Each brush is seated on the upper end and secured to a contact spring 38, the lower end of which is connected to a terminal 4% provided on the terminal plate 52. Similarly, the brush assemblies are each provided with a brush member 44 slidably mounted and projecting from the insulation plate 36. Each brush member 4- 5 is seated on and secured to the upper end of a contact spring 46, the lower end of which is connected to a terminal 43 mounted on the terminal plate 42.

Pursuant to an important aspect of the present inven tion, provision is made for a top, or upper end, loading heating chamber or melting furnace 58. As best illustrated in Figs. 6 and '7, the furnace it: is provided with a preferably metallic seat $2 at the bottom thereof. In order to mount the seat on the bar 16, provision is made for the angle brackets 5 which are bolted to the seat 52 as at as, and which are bolted to the opposite sides of the bar 16 as by the bolts The furnace is provided with an outer metal casing or housing 6t), the bottom of which is closed by the previously mentioned seat 52. As here shown, the casing 60 is cylindrical in shape and has a top Wall 62. A tapered elongated vertical rnuffie 6d has a base portion which is secured to the seat The muffle is provided with an encompassing side wall 68, the opposing sides of which diverge mutually upwardly from the base and terminate in a lip 7% which defines an upper end opening 72. Said opening 72 is in register with an opening 74 defined in the upper end Wall 62 of the casing l rovision is made on said upper wall 62 for a closure or cover 76 which is hinged thereto, as at 78, for closing the loading opening 74. An electrical resistance winding 3:; encircles the outer periphery of the muffle 64, the latter being provided with annular ribs 32. which are spaced longitudinally thereof to facilitate the positioning of the winding 80 on said outer periphery. The winding 80 is formed of a material whose resistance remains constant as the material is heated. A heating element which has a temperature coeflicient which remains constant during the heating thereof and is suitable for use in the furnace 50 is manufactured by the Kanthal Corporation of Stamford, Connecticut and is sold under the trade name Kanthal. The resistance heating element is preferably provided with a ceramic coating to prolong the life thereof. A suitable heat insulating material, indicated at 84, fills the space between the muffle and the outer wall of casing 61' Provision is made for a recess or slot 86 which is defined within the muffle for positioning a thermocouple 83. A cable 9%, which extends outwardly from the furnace 50, contains the two leads 92 and 94 of the resistance heating element :39, and the two leads 96 and 95 of the thermocouple 33. The thermocouple leads 96 and 98 are connected to the terminal connectors 100 and 102, respectively, provided on the narrower outer conducting rings 2828 and the leads 92 and 94 from the heating resistor element 80 are connected to similar terminal connectors Elli-C and 1%, provided on the heavier inner conducting rings 26-26.

A crucible 1%, preferably formed of a suitable graphitic composition, is mounted within the muflle 64. The shape of the crucible is complementary to that of the muffle. As here shown, the crucible is open at the upper end thereof, as at 198, and said opening 188 is in registry with the opening '72 in the muffle and the opening 74 at the upper end of the furnace housing 6%. The crucible is provided with a sprue 110 which extends outwardly, from the side wall thereof, through an opening 112, of complementary shape, defined in the side wall of the muflle 64, and also extends outwardly of the housing 60. More specifically, the housing is provided with an elongated cut-out 112 which extends from the side wall into the top wall thereof to accommodate the sprue 110 when the crucible is inserted therein. An insert 114 formed of suitable insulating cement is inserted through said top wall cut-out to fill the space, above and around the sprue, between the housing and the mulfle, said insert securing the sprue in position.

A cradle 116 is provided with a pair of depending legs which straddle the bar 16 and said cradle supports a flask or mold 118 between the heating chamber 50 and the flask holder 12%. The cradle may be readily disengaged from the bar by vertically lifting said cradle and the latter is longitudinally movable along said bar. It will be readily apparent that various sizes of cradles may be utilized to accommodate molds or flasks 118 of corresponding sizes. Thus, the cradle 11 6 supports the flask 118 in a disposition in which said flask is adapted to receive a charge from the heating chamber 56 through the sprue Ht) when the bar to is rotated.

The flask holder or clamping device 120 comprises a frusto-conical portion 122 which is adapted to receive therein and to engage the adjacent end of the flask 118 while the latter is engaged with the heating chamber or furnace 59. As fully illustrated and described in my copending application, holder 12 3 is provided with a depending portion 124 which is slotted, as at 126, for the reception of the bar 16, it being apparent that said holder is slidably movable along said bar toward and away from the axis of rotation of the bar. The heating chamber the flask 113 and the holder 12% are mounted on the bar 16 on one side of the axis of rotation thereof and, to counter-balance said bar, there is provided a cylindrical counterweight 128 which is slidably mounted on said bar on the opposite side of the axis of rotation thereof. The counterweight 128 is slotted, as indicated at 130, for the reception of the bar 16 and said counterweight is mounted in fixed relation with the holder 120- by means of the pair of longitudinally extending coupling.

members 132. The ends i354 of the members 132 are threadedly receivable in apertures provided in the counterweight 128. The opposite ends 136 of the members 132 are adapted to extend through suitable apertures provided in the projecting portions 138 of the holder and each of said ends 126 is rigidly secured in place by means of an associated pair of nuts 144). Therefore, it will be apparent that the holder 120 and the counterweight 128 are mounted in unitary relation for sliding movement along the bar 16 and on the rotation of said bar, the counterweight 128 will be effective to centrifugally urge the holder 12%} toward the heating member 50 for clamping the flask 118 against said chamber'in operative association therewith, as explained in my copending application. The counterweight 128 is restrained from disengagement with the bar 16 and for sliding movement therealong, by mean of a U-sl1aped part 142 which is secured to said counterweight, as fully illustrated and described in my previously identified copending application, there being provided a tension spring 144 having one end 146 secured to said part, with the opposite end 148 thereof being fixed to a part 15% carried by said bar, said spring being effective to resiliently urge the counterweight 128 away from the axis of rotation of the bar 16 so as to resiliently urge the holder 129 into clamping engagement with the flask 118. Therefore, when the bar 16 is stationary, the holder 129 will resiliently urge the flask 1E8 into operative association with the heating chamber 5%}, it bein understood that the spring 144 is a relatively weak spring and while said spring is efiicient to effect the initial clamping engagement between the flask 118 and the chamber 5%, the holder 120 may be readily retracted from the flask 118 for removing the latter from the apparatus. Once the bar 16 is released for rotation, the centrifugal force of the counter-balancing mass will urge the heating chamber 56) and flask 113 into clamped operative engagement, it being understood that the counterweight and the holder are mounted in unitary relation for sliding movement along the bar 16. Therefore, the greater the centrifugal force created by the rotation of the counterweight, the greater will be the clamping eflect of the holder.

In order to limit the movement of the counterweight toward the axis of rotation of the bar, there is provided a stop device 152 which is fixed to the bar and which is adapted to coact with a peripheral portion of the counterweight to limit the movement thereof towards said axis. The counterweight is provided with a centrally disposed upstanding shaft 154 which is adapted for the reception of one or more additional counterweights, said shaft also facilitating the winding up of the spring type motor in the base 12. Thus, suflicient counterweights may be removably stacked on the counterweight 128 to balance the mass on the opposite side of the axis of rotation of the bar 16.

Pursuant to an important aspect of the present invention, provision is made for a latch or locking device, generally indicated b, the reference number 156 in Fig. 4, for releasably latching the bar 16 in position to prevent the rotation thereof until a predetermined temperature has been reached or attained in the furnace 50. More specifically, the base 12 is provided with an auxiliary housing 158 which mounts the solenoid or winding 160 of a relay 162. The relay is provided with an armature or latch member P54 which, upon energization of the solenoid 160, is withdrawn into the relay, as indicated by the arrow 166, against the bias of a tension spring 168 which is connected at one end thereof, as at 170, to a convenient portion of the housing 158, and which is connected at the other end thereof, as at I172, to a pin 174. provided on a collar .176 carried by the latch 164-. At the upper end thereof, the armature is provided with an anti-friction roller which is adapted to engage the bar 16, in the de-energized condition of the relay i162. The housing 1% also mounts a catch 180, on which there is mounted a compression spring 182. One end of said spring abuts against-the adjacent portion 184 of the housing 158 and the other end of the spring abuts against a laterally extending pin 186 carried by the catch 180. Provision is made for a bracket member 188 which is pivotally mounted on a pivot member 190, carried by the housing 158. The bracket 188 is pivotally connected, as at 192, to one end of a link 194, the other end of which is pivotally mounted on the pin 186. The bracket 188 is provided with a clamp 196 which mounts a mercury switch 198.

in the de-energized condition of the relay 162, the various parts are disposed as illustrated in Fig. 4. It will be noted that in said condition of the parts, the free end 200 of the catch 180 abuts the collar 176, the other end of the catch being provided with a knurled finger piece 204. However, it will be understood that upon energization of the relay 162, the armature or latch 164 thereof is retracted in the direction of the arrow 166 to its inoperative position, and, when the upper surface of collar 176 clears the catch 180, the latter snap-engages in position over the collar 176, under the force of the compressed spring 182, to prevent the projection of the latch 164 to the position thereof illustrated in Fig. 4 by the spring 168 upon the subsequent de-energization of the relay 162. It will be noted, as illustrated in Figs. 2 and 4, that when the relay is in the de-energized condition thereof, so that the catch 180 is retained in its retracted position, the bracket 188 disposes the mercury switch 198 in a horizontal position so that the switch is closed between the contacts 200 and 202 thereof. However, upon energization of the relay 162, the latch 164 is retracted to permit the projection of the catch 180 by the spring 182. Said movement of the catch 180 results in the pivotal movement of the mer cury switch 198 to the broken line position thereof illustrated in Fig. 2 for opening said switch.

Provision is made for releasing the bar 16 at an exact predetermined temperature of the furnace 50. More speciiically, and as best illustrated in Fig. 8, provision is made for a pyrometer 286 which is connected through the leads 96 and 9S, and through the contact rings 28 and the cooperating brush assemblies 32, to the thermocouple 88. Said pyrometer is provided, on the casing thereof, with a light cell 208 and with a companion photoelectric cell 210, in the manner fully illustrated and described in my copending application, Serial No. 438,245, filed June 21, 1954. As illustrated and described in said latter application, the photo cell 210 is incorporated in a photoelectric control circuit which is generally indicated herein by the reference numeral 212. The light cell 203 and the photo cell 210 are adjustably mounted on the pyrometer 206 so that they may be adjusted for a predetermined position on the pyrometer which corresponds to a predetermined temperature reading on the scale thereof. As explained in said application, when the pointer or indicator 214 of the pyrometer 2 26 reaches the predetermined setting of the photo cell and the light source, the light L.

shining upon the face of the pyrometer 206 and reflected thereby to the photo cell 210 is interrupted by the indicator 214. This reduces the energization of the photo electric control circuit and results in the energization of the normally open relay 216 which is operated by said photo-electric control circuit.

As illustrated in Fig. 8, the terminal 202 of the previously mentioned mercury switch 198 is connected through the previously mentioned lead 92 and the conducting ring 26 and brush assembly 30 to one end of the resistance heating element 80, the other end thereof being connected through the other conducting ring 26 and brush assembly 30 and through the lead 94 to the lead 218 which is connected to one power line 220. The other terminal 200 of the mercury switch is connected to the other power line 222 through the lead 224. Therefore, it will be apparent that the circuit through the heater 80 is closed in the horizontal condition of the mercury switch 198 which obtains, as previously indicated when the relay 162 is tie-energized. The previously mentioned relay 216 is a normally open relay so that when the latter is energized, through the photo-electric control circuit 212, the movable contact member 226 is engaged with the stationary contact 228. As described in my latter application, when the indicator 214 reduces the energization of the photo-electric cell 210, the relay 216 is energized.

Provision is made for an alarm device 230, which in the present embodiment, is constituted by an electric buzzer. One side of the buzzer 230 is connected through the lead 232 to the stationary contact 228 of the relay 216, and when said relay is closed, said lead is connected to the lead 213 for connecting said side of the buzzer to the power line 220. The other side of the buzzer is connected to the other power line 222 through a circuit which in cludes the leads 234 and 236, the mercury switch 198 and lead 224. One side of the solenoid winding of the previously mentioned latch relay 162 is connected to the power line 222 through the circuit which includes the leads 238 and 236, the mercury switch 198 and the lead 224. The other side of said solenoid is connected to a contact 240 of the thermal delay relay 242. The companion contact 244, which is normally disengaged from the contact 240, is connected to the power line 220 through the lead 218 so as to complete the circuit through the relay 162 upon engagement of the contacts 240 and 244. One side of the heater 246, of the delay relay 242, is connected to the power line 222 through the same circuit which connects the adjacent side of the buzzer 230 thereto. The other side of the heater 246 is connected to the other power line through the lead 248, the lead 232, the relay contacts 226 and 288, in the engaged condition thereof, and the lead 218. Therefore, it will be apparent that the heater 246 is connected in parallel with the buzzer 230.

Starting with a cold mufiie 68, the apparatus of the present invention is operated as follows: The photo-electric control 210 is initially set on the pyrometer 206, opposite a reading thereof which is a predetermined temperature below the ideal casting temperature, in order to load the furnace when it is warmed up to said predetermined temperature below the ideal casting temperature. For example and not by way of limitation, the initial temperature setting may be approximately 400 below the ideal casting temperature. -If the latch 164 is in its retracted or inoperative position, the catch 180 is Withdrawn to permit the latch 164 to be projected by the spring 168 for positioning the mercury switch 198 in the closed condition thereof. The main power switch 250 is now closed for energizing the photo-electric control circuit 212 including the light cell 208 and the photo cell 210, and also for completing the circuit through the resistance heating element 80. Upon the attainment of the preset initial temperature, the indicator 214 will be in a position to reduce the energization of the photo-electric cell 210 by the light from the light source 208, which is reflected by the face of the pyrometer into the photo cell 210, as described in my latter copending application. The reduction in the energization of the photo cell operates the photoelectric control circuit 212 to energize the normally deenergized relay 216 for closing the contacts 226 and 228. This results in the energization of the buzzer 230 and also in the energization of the heater 246 of the thermal relay 242. It will be understood that the relay 242 is of the adjustable type so that it may be made to operate to close the contacts 240 and 244 after a predetermined period of time, for example and not by way of limitation, within a range of three to ten seconds. The energization of the buzzer 230 notifies the attendant that thefurnace 50 has been heated sufficiently for loading the metal therein. The attendant now opens the cover 76 at the top of the furnace and inserts the metal into the crucible 106. The buzzer continues to operate until the contacts 240244 close. The closing of said contacts results in the energization of the relay solenoid 160 whereby to withdraw the latch 164 from its projected operative position to its retracted inoperative position, the catch 180 engaging 7 said latch over the collar 176 thereof. This results in the opening of the mercury switch 198 to dc-energize the buzzer as well as the heater 246 and the heater 80. However, since the spring motor in the base 12 has not as yet been Wound, the casting apparatus does not rotate. The photo-electric cell 210 and its companion light cell 2% are now adjusted to a position on the pyrometer opposite the ideal casting temperature graduation on the scale thereof, which, as previously indicated, is preferably 400 above the first position thereof. This now results in the energization of the photo cell so that the relay 216 returns to its normally de-energized condition, the relay contacts 226, 228 being open. The shaft 154 is now rotated to wind up the spring motor in the base 12 and, before the shaft 154 is released, the catch 180 is withdrawn, against the bias of the spring 182, to permit the projection of the latch 164 to its projected position by the spring 168. This closes the switch 198 to energize the heater 80. The rod 16 is now permitted to move into engagement with the anti-friction roller 178 and the shaft 164 is released. It will be apparent that the pressure of the spring motor forces the bar against the roller 178. In this connection, it will be understood that the spring motor is wound up by rotating the shaft 154 in a clockwise direction, as indicated by the arrows in Fig. 1. Upon the attainment of the predetermined casting temperature, it will be apparent that the indicator 214, when arriving at the corresponding scale reading, will reduce the energization of the photo-electric cell 210. This will result in the energization of the relay 216 to close the contacts 226 and 228. This results in the energization of the buzzer 230 and the heater 246 of the thermal relay 242. The sounding of the buzzer 230 gives notice :or warning to the attendant that the machine or apparatus will be released for rotation Within the delay'period for which the relay 242 is adjusted, for example, within the range of 3 to 10 seconds, as the relay may be set. Therefore, the attendant will remain clear of the apparatus to prevent any possible injury to him; At the end of said delay period, the contacts 240 and 244 close to energize the relay 162. This results in the withdrawal of the latch 164 to release the bar 16 and the wound-up spring motor then rotates the apparatus. The withdrawal of the latch 164 tilts the mercury switch 198 for opening the latter whereby to open the circuits through the buzzer 230, the relay heater 246 and also the heating element 80. The latch is retained in its retracted position by the catch 180. On rotation of the bar 16, the counterweight 128, which is in fixed relation with the holder 120, will be effective to centrifugally urge the portion 122 of the holder 120 against the flask to thereby clamp the latter against the heating chamber 50, the greater the centrifugal force created by the counterweight 128, the greater will be the clamping force of the holder 120. As a result of the centrifugal action, the crucible and passes out through the sprue 11%? into the flask 118 for the casting operation.

While it is preferable to pre-heat the muflie, as previously described, prior to inserting the metal into the furnace, it will be readily apparent that this is not essential, especially in a situation where there is no excessive loss in thermal expansion of the mold resulting from the tendency of an especially small flask to lose too much heat. Under such circumstances, the photo-electric device 210 may be initially set at the predetermined casting temperature and the metal loaded into the crucible at the very beginning of the operation. The spring motor is then wound up, as previously described, so that the casting operation will take place when the pyronieter indicator reaches the predetermined casting temperature. In addition, where the mufiie is .pre-heated, as in the case where consecutive castings are made, it is not necessary to set the photo-electric control 219 to an initial temperature which ;is' below the ideal casting temperature. In the latter situation, the photo-electric control is initially set molten metal climbs up the sides of the e the furnace temperature, and

8 t to the casting temperature, the metal is loaded into the crucible and the spring motor is wound up and latched in position, as previously described.

The use of the contact rings 2626 and 28-28 and the brushes 3434, 44- 34 is advantageous in that they provide for a casting apparatus which has a much longer life than one using separable contacts by eliminating the sparking and the resultant pitting and wear associated with separable contacts. Moreover, if separable contacts were used for the heater 89, it would be necessary, before permitting the furnace to rotate, to first tilt the mercury switch 198 to de-energize heater 8!), then to disengage the separable contacts and finally to release the bar 16 for rotation. The use of the rings and brushes permits for the concomitant tilting of the switch 198 and the release of the bar 16 for rotation thereof.

From the above, it will be apparent that the present invention provides for an automatic casting operation at a predetermined exact temperature, as indicated by the exact reading'on the pyrometer. In addition, provision is made for a top loading furnace. This greatly increases the ease and facility with which the furnace may be loaded, as compared with a side loading furnace. This also greatly increases the capacity of the furnace, as compared to a side loading furnace, since in the case of a side loading crucible, a thick lip was required heretofore at the bottom of the crucible, at the loading side thereof, so that the molten metal would not flow out from the loading side thereof. This resulted in a smaller opening at the loading side, which made the crucible harder to load and which also'limited the amount that could be loaded into the crucible.

While I have shown and described the preferred embodiment of my invention, it will be understood that various changes may be made in the present invention Without departing from the underlying idea or principles of the invention within the scope of the appended claims.

Having'thus described my invention, what I claim and desire to secure by Letters Patent is: e

1. In a centrifugal casting apparatus, a centrifugally rotatable furnace, heating means for said furnace, biased latching means normally prevent rotation of said furnace, means for indicating the temperature of said furnace, and means operable in response to a predetermined indication of said indicating means for releasing said furnace from said latching means for rotation thereof, alarm means, and means to energize said alarm means a predetermined time period prior to the release of said furnace.

2. In a centrifugal casting apparatus, a centrifugally rotatable furnace normally retained against rotation, heating means for said furnace, a meter for indicating the furnace temperature, and photo-electric control means operable in response to a predetermined meter reading to release said furnace for a casting operation.

3. in a centrifugal casting apparatus, a centrifugally rotatable furnace normally retained against rotation, heating means for the furnace, meter means for indicating means operable in response to a predetermined meter indication to release said furnace for a casting operation, and Warning means operable for a predetermined period prior to the release of said furnace.

4. In a centrifugal casting apparatus, a centrifugally rotatable furnace normally retained against rotation there of, means for heating said furnace, and photo-electric means operable in response to a predetermined furnace temperature for releasing said furnace to perform a casting operation.

5. In a centrifugal casting apparatus, a centrifugally rotatable furnace, a heating circuit for said furnace, means normally latching said furnace against rotation thereof, relay means associated with said latching means, normally closed switch means in said heating circuit, and photo-electric control means operable in response to a 9 predetermined furnace temperature to operate said relay means for disengaging said latching means from said furnace and to simultaneously open said switch means to open the heating cincuit.

6. In a centrifugal casting apparatus, a centrifugally rotatable furnace, a heating circuit for said furnace, means normally latching said furnace against rotation thereof, relay means associated with said latching means, means for delaying the energization of said relay means for a predetermined period, normally closed switch means in said heating circuit and operable by said latching means, warning means, and photo-electric control means, operable in response to a predetermined furnace temperature to energize both said warning means and said delaying means, whereby, upon the energization of said relay means by said delaying means, said relay means operates said latching means to release said furnace and the latching means operates said switch means to open the heating circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,015,818 McManus Jan. 30, 1912 1,502,435 Morgan July 22, 1924 1,751,846 Wilkes Mar. 25, 1930 1,823,037 Fm'tzsche Sept. 15, 1931 2,142,602 Blethen Jan. 3, 1939 2,197,514 Barnes Apr. 16, 1940 2,209,381 Berger July 30, 1940 2,375,463 Berger May 8, 1945 2,430,171 Hatch Nov. 4, 1947 2,451,103 Loew Oct. 12, 1948 2,637,079 Kemppe May 5, 1953 2,749,585 Prosen June 12, 1956 

